Laboratory instruments of a kind discussed herein serve, for example, as analytical balances in many fields of industry. Such fields of industry may include, without limitation, laboratories of research and development departments, as well as production areas (e.g., for quality control).
One exemplary analytical balance with a weighing compartment is described in detail in U.S. Pat. No. 4,700,793 A. Generally speaking, analytical balances are balances with a very high resolution of the measurement result. Consequently, even the smallest extraneous factors acting on the object being weighed or on the load receiver of the balance can introduce an error in the weighing result. The extraneous influence factors are rarely stable and this can lead to a situation where the precise weight of the weighing object cannot be determined. To protect the weighing system from being influenced by the environment, a weighing compartment is therefore commonly enclosed with a so-called draft protection device.
As shown in U.S. Pat. No. 4,700,793 A, the typical draft protection device of an analytical balance has in most cases two slidable sidewalls and sometimes also a slidable top cover, as the object to be weighted is normally delivered to the load receiver of the balance from the side, and sometimes also from above. A front wall of the draft protection device is normally rigidly connected to the housing of the balance and, by functioning as a structural support, lends stability to the draft protection device. A draft protection device needs to be as tightly closed and solid as possible, so that air drafts of the ambient atmosphere cannot propagate into the weighing compartment through gaps and openings of the draft protection device and cause atmospheric disturbances in the weighing compartment.
In order to make the weighing compartment, and in particular, the sidewalls of the draft shield easier to clean, a draft shield is proposed in U.S. Pat. No. 6,686,545 B2 whose front wall and sidewalls can be released from a form-fitting seat through a tilting movement and subsequently removed from the balance by a pulling movement. The top cover is connected through a linear guiding constraint to the balance housing, which serves as rear wall. The top cover can be slid horizontally over the balance housing, whereby the draft shield is opened at the top. In addition, the top cover, too, can be separated from the linear guiding constraint by means of a tilting movement.
All of the balances described above are equipped with a draft protection device whose sidewalls are at their top edges and bottom edges guided for horizontal movement along the housing of the draft protection device or of the balance itself. This arrangement has the disadvantage that in spite of all preventive measures, traces of weighed substances can accumulate in the lower guide tracks or guide parts. In order to prevent substances from being spread around, the lower guide tracks or guide parts have to be cleaned periodically with careful attention and at considerable cost.
It would therefore be desirable to provide a draft protection device for a laboratory instrument, wherein at least one openable sidewall thereof works without guiding constraints or guide parts in the area of its bottom edge, and wherein the draft protection device is designed in such a way that in its closed state it is as tight and stable as possible so that air movements of the ambient environment are not transmitted through gaps and openings into the weighing compartment of the instrument.